1. Field of the Invention
The present invention relates to an optical printer head and an image forming apparatus.
2. Related Background Art
Conventionally, an optical printer head, such as an LED array head, is employed as exposure means for an image forming apparatus, such as an electrophotographic printer.
FIG. 4 is a schematic diagram showing the configuration of an electrophotographic printer.
In FIG. 4, the electrophotographic printer includes a photosensitive drum 101, a charging device 102, an LED array head 103, a developing device 104, a transfer device 105, a charge elimination device 106, a cleaning device 107 and a sheet feeding device 108.
When the photosensitive drum 101 is exposed to light after a charge has been placed on the surface of the photosensitive drum 101, a latent image, consonant with the light, is formed on the surface. In this case, the photosensitive drum 101 is rotated in a direction indicated by an arrow A.
The charging device 102, through the discharge of electrons, places a negative charge having a predetermined potential on the surface of the photosensitive drum 101.
The LED array head 103 includes a plurality of LEDs, linearly arranged, and a lens for controlling light emitted by the LEDs. Individual LEDs in the LED array head 103 emit light selectively, based on externally received image data, to irradiate the surface of the photosensitive drum 101, which carries a charge having a predetermined potential, and to form a latent image thereon.
The developing device 104 then develops the latent image formed on the photosensitive drum 101 by generating a toner image (a picture image), and the transfer device 105 transfers the toner image from the photosensitive drum 101 to a recording sheet 109 fed by the sheet feeding device 108.
Thereafter, the charge elimination device 106 removes the charge from the surface of the photosensitive drum 101, and the cleaning device 107 cleans the surface of the photosensitive drum 101.
In an image forming apparatus employing an optical printer head, oxygen molecules in the air are ionized by the discharge of the charging device 102 and ozone is generated.
Ozone reacts with nitrogen in the air to produce a nitrogen compound and this nitrogen compound combines with water in the air and becomes nitric acid. Nitric acid chemically reacts with an alkali component on the surface of the lens of the optical printer head and becomes potassium nitrate, which is attached to the surface of the lens and causes the lens of the optical printer head to be clouded over.
When the lens of the optical printer head is clouded over; the light emitted by the optical printer head is partially blocked, and is dimmer. Accordingly, since the intensity of the light projected onto the photosensitive drum is thereby reduced, a blurred image is produced.
In patent document 1 (Japanese Patent Laid-Open Publication No. 2001-171171), an image forming apparatus is described that can prevent the dimming of light at the lens of an optical printer head.
The image forming apparatus in patent document 1 includes an LED array head having a lens that is covered with a photo catalyst layer. The photo catalyst layer is activated when irradiated with light, and induces the decomposition of an organic material that is attached to the outer surface of the lens.
When, however, a photo-catalyst layer is employed to prevent the dimming of light at the lens, an optical printer head, and an image forming apparatus that employs this optical printer head, becomes expensive.